Apparatus for imaging particles in a liquid flow

ABSTRACT

An apparatus for imaging and analyzing particle components in a sample liquid flow containing particle components such as blood and urine, or fine particles of organic high polymer in suspension or the like. A conventional particle imaging flow cytometer is combined with a light source such as a lamp with small coherence, and an image intensifier with gate function of high response, so that a clear particle image without a deflection or interference fringe is obtained. Thus, in the apparatus having the still imaging function, by using the image intensifier with a high speed gate function, even with a light source of a long luminous time such as a lamp, a clear still image of a particle flowing at high speed is obtained.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for imaging particles in aliquid flow, and in particular to an imaging flow cytometer for imagingand analyzing particle components in a sample liquid containing particlecomponents such as blood and urine, or fine particles such as organichigh polymer particles in suspension, or the like, and more particularlyto an imaging flow cytometer capable of obtaining a clear still image ofparticles flowing at high speed (for example, 5 m/sec. or more) evenwith a light source of a long light emission time such as a lamp, byusing an image intensifier with a high speed gate function, in a flowcytometer with still imaging function.

To image particles in a sample liquid flowing at a high speed of severalmeters per second in a flow cell, using a flow cytometer, asconventionally shown in FIG. 1, it is generally know to capture aparticle image free of vibration, by the combination of a pulse laserlight source 29 capable of emitting an intense light only for a momentand a video camera 43. In a flow cell 14, a sheath flow 15 is formed bypassing sheath liquid around the sample flow including the particles 16to be detected, and this sample fine flow 15 is illuminated with laserlight from an argon laser generator 10. The light signal (the scatteredlight or fluorescent light) from the particle is detected by a lightdetector (photo-multiplier or the like) 22, and a signal S1 is sent to asignal processing unit 24 to be processed, thereby analyzing theparticles. The sheath flow is a flow covered with a laminar sheathliquid around the suspension of particles in order to pass the particlesneatly in one row precisely in the middle of the liquid flow. Also shownin FIG. 1 is a pulse emission trigger signal S4, a laser power supply27, an image processing unit 46, condenser lenses 12, 31, objectivelenses 20, 33, a projection lens 41, and a beam stopper 18.

In the Japanese Laid-open Patent Sho. 62-254037, it is disclosed toimage only particles with specific characteristics, by detecting theparticles by the image pickup device nearly simultaneously, by providingthe flow cytometer with a streak image pickup device, and processing theimaging signal only when matched with a predetermined characteristicvalue. It is also disclosed to use a high sensitivity camera and acamera tube as the image pickup device, and picture the entire imageinstantly.

The Japanese Laid-open Patent Sho. 63-94156 discloses a flow cytometerin which the light source for detecting particles is always illuminated,passing of a cell is detected by a cell detector, and after delaying fora specific time in a delay circuit, the light source for the laser pulsefor imaging is turned on to picture the cell.

In the conventional particle imaging flow cytometer shown in FIG. 1,sine the laser light source possesses a high coherence, the interferencefringe is often obvious in the obtained particle image, so that theimage quality is not so high. Besides, since the laser light sourcepresents a monochromatic light, a color image of the particles is notobtained. Besides, the pulse laser light source, of the gas type, islarge in size, and the power source is also large in scale, and is veryexpensive.

By using a xenon flash lamp small in coherence as the light source, aclear image without an interference fringe may be obtained, but theluminous time of the xenon flash lamp is generally long, 1 μsec or more,and in this case the image may deviate unless the sheath flow velocityis 0.3 m/sec. or less. At the flow velocity of 0.3 m/sec., however, theintrinsic high processing ability of the flow cytometer, that is, thelarge number of cells analyzed per unit of time is not achieved.

Besides, neither publication refers to imaging of still pictures ofparticles by using in image intensifier with high speed gate, which is afeature of the present invention.

OBJECT AND SUMMARY OF THE INVENTION

It is hence a primary object of the present invention to provide anapparatus capable of obtaining a clear particle image without deflectionor on interference fringe, by combining the optical system of theconventional particle imaging flow cytometer with a lamp of smallcoherence and an image intensifier with a gate function capable ofresponding at high speed.

To achieve the above object, the present invention provides a firstimaging flow cytometer for forming a sheath flow by passing sheathliquid around a sample flow containing particles to be detected,emitting light to this sample fine flow, detecting light signals fromthe particles, processing the signals in a signal processing unit, andanalyzing the particles, comprising:

a light source for imaging particles by emitting incoherent light, thatis, light which does not induce interference, to a sample fine flowregion downstream of the detecting region of the particle detectinglight,

an image intensifier to be focused by the transmission light of theparticles in the sample fine flow region,

a video camera for capturing the image of the output plane of the imageintensifier, and

an image processing unit for processing the video signal from the videocamera, wherein

the image intensifier is an image intensifier provided with a high speedgate, and

the signal processing unit generates a trigger signal S2 for emittingthe light from the light source for imaging a particle by delaying aspecific time from detection of the particle signal S1, and while thelight source is radiating, a gate signal S3 for opening the shutter ofthe image intensifier is generated.

The present invention presents a second imaging flow cytometer, inwhich, in the first apparatus, the light source for imaging particles isalways radiated, and the signal processing unit generates a gate signalS3 for opening the shutter of the image intensifier by a specific timedelay from the detection of particle signal S1.

The present invention also presents a third imaging flow cytometer forforming a sheath flow by passing sheath liquid around a sample flowcontaining particles to be detected, emitting light to this sample fineflow, detecting light signals from the particles, processing the signalin a signal processing unit, and analyzing the particles, comprising:

a light source for image particles for emitting incoherent light to thesample fine flow region downstream of the detection region of theparticle detecting light,

spectral means for dividing the transmission light of the particles inthe sample fine flow region into components of three wavelength regionsof red, green and blue,

image intensifiers to be focused by the transmission lights divided inthree components,

video cameras for capturing the images of output planes of the imageintensifiers, and

an image processing unit for processing the video signals from the videocameras as signals R, G, B, wherein

the image intensifiers are image intensifiers provided with high speedgates, and

the signal processing unit generates a trigger signal S2 for emittingthe light from the light source for imaging a particle by delaying for aspecific time from the detection of the particle signal S1, and whilethe light source is being radiated, a gate signal S3 for opening theshutters of the image intensifiers is generated.

The present invention also presents a fourth imaging flow cytometer, inwhich, in the third apparatus, the light source for imaging particles isalways radiated, and the signal processing unit generates a gate signalS3 for opening the shutters of the image intensifiers in a specific timedelay from the detection of the particle signal S1.

The apparatus of the present invention comprises two systems, that is,the particle detecting system and the particle imaging system. Theparticle imaging system is installed at the downstream side of theparticle detecting system in the sample fine flow. When the particledetection signal S1 is detected, the signal processing unit generates atrigger signal S2 in a specific time delay, and the light source forimaging a particle is illuminated to capture a still image of theparticle passing through the sample fine flow by a video camera. Thedelay of a specific time is the time required for the particle to movefrom the particle detection region to the imaging region.

In order to obtain a still image of the particle flowing at high speed,the luminous time must be short. If the luminous time is long, a blurryimage is captured. Besides, a sufficient quantity of light is alsoneeded.

In the present invention, by generating a gate signal S3 while theparticle imaging light source is emitting light, the image intensifieris operated to obtain a still image of the particle. The imageintensifier intensifies the input feeble image, and produces a brightimage. The image intensifier with a high speed gate function operates asan image intensifier only when the gate signal is ON. Accordingly,regardless of the luminous time of the light source, by turning on thegate signal for a short time while the light source is luminous, abright and sharp still image is obtained. The still picture obtained bythe image intensifier is captured by the video camera, and processed inthe image processing unit.

In the third apparatus of the present invention, the transmission lightis divided into red, green and blue components, and for these threeimages there are three image intensifiers with a high speed gate andthree monochromatic video cameras so that video signals of R, G, Bcomponents are obtained for one image. That is, one color image isobtained.

In the second and fourth apparatus, by always emitting the imaging lightsource, by operating the image intensifier by the gate signal S3 onlywhen desired to capture, a still image is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic explanatory diagram of a conventional apparatus.

FIG. 2 is a schematic explanatory diagram showing an embodiment of animaging flow cytometer of the present invention.

FIG. 3 is a schematic explanatory diagram showing another embodiment ofan imaging flow cytometer of the present invention.

FIG. 4 is a diagram for explaining the timing of each signal in animaging flow cytometer of the present invention.

FIG. 5 is a diagram for explaining the structure and operating principleof an image intensifier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, some of the preferred embodiments of thepresent invention are described in detail below.

FIG. 2 shows an imaging flow cytometer for forming a sheath flow bypassing sheath liquid around a sample flow containing particles 16 to bedetected, emitting light to this sample fine flow 15, detected lightsignals from the particles, processing the signals in a signalprocessing unit 24, and analyzing the particles, comprising:

a light source 28 for imaging particles by emitting incoherent light,that is, light which does not induce interference, to a region of thesample fine flow downstream of the detecting region of the particledetecting light,

an image intensifier 38 to be focused by the transmission light of theparticles in the sample fine flow region,

a video camera 42 for capturing the image of the output plane of theimage intensifier 38, and

an image processing unit 44 for processing the video signal from thevideo camera 42, wherein

the image intensifier 38 is an image intensifier provided with a highspeed gate, and

the signal processing unit 24 generates a trigger signal S2 for emittingthe light from the light source 28 for imaging a particle by delaying aspecific time from detection of the particle signal S1, and while thelight source 28 is illuminating, a gate signal S3 for opening theshutter of the image intensifier 38 is generated.

In the imaging flow cytometer rated immediately above, the light source28 for imaging particles is always radiated, and the signal processingunit 24 generates a gate signal S3 for opening the shutter of the imageintensifier 38 by a specific time delay from a the detection of theparticle signal S1.

FIG. 3 shows an imaging flow cytometer for forming a sheath flow bypassing sheath liquid around a sample flow containing particles 16 to bedetected, emitting light to a sample fine flow 15, detecting lightsignals from the particles, processing the signal in a signal processingunit 24, and analyzing the particles, comprising:

a light source 28 for imaging particles for emitting incoherent light toa region of the sample fine flow downstream of the detection region ofthe particle detecting light,

spectral means 35 for dividing the transmission light of the particlesin the sample fine flow region into components of three wavelengthregions of red, green and blue,

image intensifiers 38a, 38b, 38c to be focused by the transmitted lightdivided in three components,

video camera 42a 42b, 42c for capture the images of the output planes ofthe image intensifiers 38a, 38b, 38c, and

an image processing unit 45 for processing the video signs from thevideo cameras 42a, 42b, 42c as signals R, G, B, wherein

the image intensifiers 38a, 38b, 38c are image intensifiers providedwith high speed gates, and

the signal processing unit 24 generates a trigger signal S2 for emittingthe light from the light source 28 for imaging a particle by delayingfor a specific time from the detection of the particle signal S1, andwhile the light source 28 is being radiated, a gate signal S3 foropening the shutters of the image intensifiers 38a, 38b, 38c isgenerated.

In the imaging flow cytometer rated immediately above, the light source28 for imaging particles is always radiated, and the signal processingunit 24 generates a gate signal S3 for opening the shutters of the imageintensifiers 38a, 38b, 38c in a specific time delay from the detectionof the particle signal S1.

The apparatus of the present invention comprises two systems, that is,the particle detecting system and the particle imaging system. Theparticle imaging system is installed at the downstream side of theparticle detecting system in the sample fine flow 15. When the particledetection signal S1 is detected, the signal processing unit 24 generatesa trigger signal S2 in a specific time delay, and the light source 28for imaging a particle is illuminated to capture a still image of theparticle passing through the sample fine flow by a video camera 42. Thespecific time delay is the time required for the particle to move fromthe particle detecting region to the image capturing region.

In order to obtain a still image of the particle flowing at high speedthe luminous time must be short. If the luminous time is long, a blurryimage is captured. Besides, a sufficient quantity of light is alsoneeded.

In the present invention, by generating a gate signal S3 while theparticle imaging light source 28 is emitting light, the imageintensifier 38 is operated to obtain a still image of the particle. Theimage intensifier intensifies the input feeble image, and produces abright image. The image intensifier with a high speed gate functionoperates as an image intensifier only when the gate signal is ON.Accordingly, regardless of the luminous time of the light source, byturning on the gate signal for a short time while the light source isluminous, a bright and sharp still image is obtained. The still imageobtained by the image intensifier is captured by the video camera 42,and processed in the image processing unit 44.

In the apparatus of FIG. 3, the transmission light is divided into red,green and blue components, and for these three images there are threeimage intensifiers 38a, 38b, 38c each with a high speed gate and threemonochromatic video cameras 42a, 42b, 42c, so that video signals of R,G, B components are obtained for one image. That is, one color image isobtained.

In the apparatus of FIGS. 2 and 3, a still image is obtained by alwaysemitting the imaging light source 28, by operating the image intensifierby the gate signal S3 only when desired.

The apparatus of FIG. 2 is realized by combining the conventional imageflow cytometer shown in FIG. 1 with the light source 28 for imaging aparticle for emitting incoherent light, and the image intensifier 38with high speed gate to be focused by the transmission light ofparticles, and others.

As an example of the light source 28 which is small in coherence, axenon lamp or a halogen lamp may be used, and the lamp may be either ofthe flash emission type or of the continuous emission type.

The sample flow containing the particle 16 to be detected is led into aflow cell 14 composed of a transparent material such as glass andplastic, and a sheath liquid is supplied to cover the circumference ofthe sample flow, thereby forming a sheath flow The laser light from thelaser light source 10 is emitted to the sample fine flow 15 through thecondenser lens 12. The light signal (scattered light or fluorescentlight) from the particle is detected by the light detector 22 throughobjective lens 20 and beam stopper 18, and the signal S1 is sent to thesignal processing unit 24 to be processed. The strobe luminous triggersignal S2 from the signal processing unit 24 is sent to the power supplyof strobe 26 to emit the light from the light source 28 for imaging aparticle, and incoherent light is emitted to the sample fine flow regiondownstream of the detection region of the particle detection lightthrough collimator lens 30 and condenser lens 32. The light transmissionfrom the particle passes through the objective lens 34 and theprojection lens 36, and is focused on the photoelectric plane (inputplane) of the image intensifier 38 with high speed gate function. Theimage of the output plane of the image intensifier 38 is projected tothe video camera 42 through relay lens 40 to be captured, and the videosignal is sent to the image processing unit 44 to be processed.

FIG. 5 is a diagram for explaining the operating principle of the imageintensifier 38. The gate function of the image intensifier 38 isrealized generally by polarity control of the potential of thephotoelectric plane 50 against the microchannel plate (MCP) 56. That is,when the potential of the photoelectric plane 50 is positive, thephotoelectrons released from the photoelectric plane 50 not reach theMCP 56, and it thereby serves as a shutter in a closed state. On thecontrary, when the potential of the photoelectric plane 50 is negative,the photoelectrons reaches the MCP 56, and the shutter is opened. Thisresponse of the gate function is usually as fast as several nanoseconds.Numerals 52, 54 are electronic lenses, and 58 is a fluorescent plane.

Supposing the sheath flow velocity to be 5 m/sec. and the allowance ofimage deflection to be 0.3 μm, the exposure time to the CCD plane of thevideo camera is 60 nsec. or less. Hence, by setting the gate ON timewithin 60 nsec., a deflection-free particle image is obtained.

If taken by using an ordinary lamp and video camera in a short exposuretime of 60 nsec. or less, only an almost black image is obtained, but byadding the image intensifier 38 having a light amplification power of athousand to tens of thousands of times, a bright image is obtained.

The control of the timing for turning on the gate of the imageintensifier 38 is explained by reference to FIG. 4. From the scatteredlight or signal S1 of fluorescent intensity obtained from the detectionsystem as the convention flow cytometer, the particle is detailedpassing through the detection area of the flow cell 14. Next, waitinguntil the particle reaches the video camera capturing area located inthe downstream direction of the detection area, the gate of the imageintensifier 38 is turned on for a period of scores of nanoseconds. Whenusing a lamp of the flash emission type, first a trigger forilluminating the flash is applied, then the gate is turned on. The timefrom the issue of the trigger for lighting the flash till the gate ofthe image intensifier 38 is turned on depends on the delay time t1 fromthe issue of the trigger to the lamp till the emission intensity Lreaches the peak. Meanwhile, S2 is a strobe luminous trigger signal, S3is a gate ON signal of image intensifier, and tm is the time that theparticle moves from the laser detection area to the video cameracapturing area.

By turning on the gate of the image intensifier 38, photoelectronsdepending an the particles image focused on the photoelectric plane 50are released, and these photoelectrons are put into the MCP(microchannel plate) 56, and are amplified several thousand times. Theamplified photoelectrons further excite the fluorescent plane 58 whichis the output plane, and a particle image amplified several thousandtimes is obtained. The image on the fluorescent plane 58 is focused onthe CCD plane of the video camera 42 through the relay lens 40 oroptical fiber.

The video camera 42 is available in the field cumulative type and framecumulative type depending on whether the light cumulative time is 1/60sec. or 1/30 sec., and where the vertical resolution is more important,the frame cumulative type should be used. In this case, in order toobtain a satisfactory particle still image, the exposure time by thegate function is limited to only one exposure in an even-number fieldperiod. One exposure means multiple exposures are prohibited. Therefore,all particles passing through the flow cell detection unit cannot betaken, and an application for taking a specific particle only isdesired.

As the light source 28 for particle imaging, by using a white lightsource such as xenon lamp or halogen lamp, a color image of the particledifficult to obtain in the conventional laser light source can beobtained. An embodiment for this purpose is shown, in FIG. 3. Three setseach of image intensifiers each with a gate function and monochromaticvideo cameras are provided, and filters or prisms for separating(resolving) the light from the particle into the three primary colors ofred, green and blue are disposed before the input planes of theindividual image intensifiers 38a, 38b, 38c, and the image is amplifiedin each color and is captured by the video cameras 42a 42b, 42c. Thevideo signals from the individual video cameras are obtained as colorvideo signals of R (red), G (green) and B (blue). Numerals 35a, 35b, 35care spectral means (for example, dichroic mirrors), and 36a, 36b, 36care projection lenses, 40a, 40b, 40c are relay lenses, and 45 is animage processing unit. The other components and their function are sameas in FIG. 2.

The present invention, being thus constructed, brings about thefollowing effects.

(1) Using the image intensifier with a high speed response gate, ablur-less, clear particle image of a particle flowing at high speed isobtained by a lamp light source of a relatively long luminous time suchas xenon lamp, without using a pulse laser light source of shortluminous time and a large quantity of light.

(2) Since an incoherent light source such as a xenon lamp is used as thelight source, a particle image without interference fringe may beobtained. The lamp is an inexpensive and small light source, and theapparatus may be reduced in cost and in size.

(3) When the particle image is separated into red, green and blue light,and image intensifiers and video cameras are provided for individualimages, a color image which was difficult to obtain in the monochromaticlight (laser light source) can be obtained.

(4) In the apparatus of FIGS. 2 and 3, a blurless, sharp image isobtained even if the light source for particle imaging is alwaysradiated.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments, and that various changesand modifications may be effected therein by one skilled in the artwithout departing from the scope or spirit of the invention as definedin the appended claims.

What is claimed is:
 1. An apparatus for imaging particles in a liquidflow, the liquid flow forming a sheath flow by passing a sheath ofliquid around a sample flow containing particles to be detected,emitting light to the sample flow, detecting light signals from theparticles, processing the signals in a signal processing unit, andanalyzing the particles, comprising:a light source for illuminatingparticles by emitting incoherent light which does not induceinterference, to a sample flow region of the liquid flow; an imageintensifier for receiving the transmitted light of the particles in thesample flow region, for intensifying an input, feeble image, andproducing a bright image, said image intensifier having a shutter; avideo camera for capturing the image of the image intensifier andgenerating a video signal; an image processing unit for processing thevideo signal from the video camera; a signal processing unit; anddetecting means for detecting the existence of particles in the sampleflow region and generating a particle signal S1; wherein: the imageintensifier is an image intensifier provided with a high speed gate; andthe signal processing unit generates a trigger signal S2 for emittingthe light from the light source for illuminating a particle on the basisof the detection of the particle signal S1, and while the light sourceis radiating, generating a gate signal S3 for opening the shutter of theimage intensifier.
 2. An apparatus for imaging particles in a liquidflow of claim 1, wherein the light source for illuminating particles isalways radiated, and the signal processing unit generates the gatesignal S3 for opening the shutter of the image intensifier on the basisof the detection of the particle signal S1.
 3. An apparatus for imagingparticles in a liquid flow for forming a sheath flow by passing a sheathof liquid around a sample flow containing particles to be detected,emitting light to the sample flow, detecting light signals from theparticles, processing the signals in a signal processing unit, andanalyzing the particles, comprising:a light source for illuminatingparticles for emitting incoherent light to a sample flow region of theliquid flow; spectral means for dividing the transmitted light of theparticles in the sample flow region into components of three wavelengthregions of red, green and blue; a plurality of image intensifiers forreceiving the transmitted light from a respective one the divided threecomponents, each image intensifier having a shutter; a plurality ofvideo cameras for capturing the images of a respective image intensifierand each generating a video signal; an image processing unit forprocessing the video signals from the video cameras as signals R, G, B;a signal processing unit; and detecting means for detecting theexistence of particles in the sample flow region and generating aparticle signal S1; wherein; the image intensifier is an imageintensifier provided with a high speed gate; and the signal processingunit generates a trigger signal S2 for emitting the light from the lightsource for illuminating a particle on the basis of the detection of theparticle signal S1, and while the light source is being radiated,generating a gate signal S3 for opening the shutters of the imageintensifiers.
 4. An apparatus for imaging particles in a liquid flow ofclaim 3, wherein the light source for illuminating particles is alwaysradiated, and the signal processing unit generates the gate signal S3for opening the shutters of the image intensifiers on the basis of thedetection of the particle signal S1. .Iadd.5. An apparatus for imagingparticles in a liquid flow, the liquid flow forming a sheath flow bypassing a sheath of liquid around a sample flow containing particles tobe detected, emitting light to the sample flow, detecting light signalsfrom the particles, processing the signals and analyzing the particles,comprising:a light source for illuminating particles by emitting lightto a sample flow region of the liquid flow; an image intensifier forreceiving light of the particles in the sample flow region, forintensifying an input, feeble image, and producing a bright image, saidimage intensifier having a shutter; a video camera for capturing theimage of the image intensifier and generating a video signal; an imageprocessing unit for processing the video signal from the video camera;and a signal processing unit wherein:the image intensifier is an imageintensifier provided with a high speed gate; and the signal processingunit generates a gate signal for opening the shutter of the imageintensifier. .Iaddend..Iadd.6. An apparatus for imaging particles in aliquid flow, the liquid flow forming a sheath flow by passing a sheathof liquid around a sample flow containing particles to be detected,emitting light to the sample flow, detecting light signals from theparticles, processing the signals, and analyzing the particles,comprising:a light source for illuminating particles by emitting lightto a sample flow region of the liquid flow; an image intensifier forreceiving light of the particles in the sample flow region, forintensifying an input, feeble image, and producing a bright image, saidimage intensifier having a shutter; a video camera for capturing theimage of the image intensifier and generating a video signal; an imageprocessing unit for processing the video signal from the video camera; asignal processing unit; and detecting means for detecting the existenceof particles in the sample flow region and generating a particle signalwherein:the image intensifier is an image intensifier provided with ahigh speed gate; and the signal processing unit generates a gate signalfor opening the shutter of the image intensifier. .Iaddend..Iadd.7. Anapparatus for imaging particles in a liquid flow of claim 6, wherein thelight source for illuminating particles is always radiated, and thesignal processing unit generates the gate signal for opening the shutterof the image intensifier on the basis of the detection of the particlesignal. .Iaddend..Iadd.8. An apparatus for imaging particles in a liquidflow, the liquid flow forming a sheath flow by passing a sheath ofliquid around a sample flow containing particles to be detected,emitting light to the sample flow, detecting light signals from theparticles, processing the signals, and analyzing the particles,comprising:a light source for illuminating particles by emitting lightto a sample flow region of the liquid flow; an image intensifier forreceiving light of the particles in the sample flow region, forintensifying an input, feeble image, and producing a bright image, saidimage intensifier having a shutter; a video camera for capturing theimage of the image intensifier and generating a video signal; an imageprocessing unit for processing the video signal from the video camera; asignal processing unit; and detecting means for detecting the existenceof particles in the sample flow region and generating a particle signalwherein:the image intensifier is an image intensifier provided with ahigh speed gate; and the signal processing unit generates a triggersignal for emitting the light from the light source for illuminating aparticle on the basis of the detection of the particle signal, and whilethe light source is radiating, generating a gate signal for opening theshutter of the image intensifier. .Iaddend..Iadd.9. An apparatus forimaging particles in a liquid flow of claim 8, wherein the light sourcefor illuminating particles is always radiated, and the signal processingunit generates the gate signal for opening the shutter of the imageintensifier on the basis of the detection of the particle signal..Iaddend.